Brazil was jolted on Saturday by a fourth fatal World Cup stadium accident when a young construction worker fell to his death, heightening safety worries six months from the start of the tournament.

The latest fatality, at the Manaus Arena in the northern Amazonia region, will add scrutiny to the host nation's preparations, with some stadiums behind schedule and extra shifts being worked in a push to be ready for the soccer extravaganza.

Marcleudo de Melo Ferreira plunged 35 meters (115 feet) in the early hours while working on the roof of the $200 million, 42,000-seat capacity arena.

He was taken to hospital but died just before dawn.

Brazilian media reported the 22-year-old fell after a cable broke as he prepared to finish a night shift. The venue is currently 93 percent complete and has around 1,900 people working around the clock to finish its construction.

The accident brought to five the number of deaths at event sites, and comes two weeks after two people died at the Sao Paulo stadium scheduled to host the June 12 opening match between Brazil and Croatia.

In an unrelated incident, a construction worker died of a heart attack while working on a new convention center near the stadium amid allegations from his family that he was overworked.

Saturday's stadium death was the second fatality at Manaus Arena, which will host England's opening match on June 15 against Italy, plus three other World Cup matches.

After the first death in the tropical city's stadium, the state public prosecutor demanded dozens of upgraded security measures, but there has been no word on any progress.

A January report found working conditions were unsatisfactory amid claims workers had not been issued sufficient safety equipment.

FIFA, which has played down concerns over stadium delays, expressed its sadness at the latest construction death.

"We would like to send our most sincere condolences to his family, relatives, colleagues and friends," soccer's governing body said in a statement.

In addition to the two Manaus accidents and the double fatality in Sao Paulo - a venue that organizers say will only be completed in mid-April - a death occurred at a new stadium in Brasilia last year.

Manaus was a controversial choice for a new multimillion-dollar stadium, not least because there is no top club in the area to attract fans after the 2014 event.

In September, one local official suggested the venue might even be turned into a processing center for prisoners for fear it could otherwise become an expensive relic.

Further controversy came following last week's World Cup draw when the mayor of Manaus criticized England coach Roy Hodgson for saying he wanted to "avoid" the venue.

Hodgson indicated he in fact wanted his team to be spared the strength-sapping humidity of the region, particularly since the game has been moved ahead from an evening start to late afternoon to suit European television schedules.

Construction firm Andrade Gutierrez promised to immediately open an investigation into the latest accident.

"We reiterate our commitment to ensuring the security of everyone working at the site," the company said in a statement, noting work had been halted as a mark of respect to the dead man.

"We deeply regret the accident."

A spokesman said the dead man had been working for a company subcontracted to build the venue's overhead covering.

Local construction union leader Cicero Custodio told the G1 news portal that workers were ready to strike if conditions did not improve.

"Workers at the Amazonia Arena are being ill-treated," said Custodio.

"We are being ignored by the authorities. I have been talking about conditions at the arena and the risks of night work for some time.

"Ideally, there would be a general strike to show how things really are," said Custodio.

Manaus coordinator Miguel Capobiango Neto has promised the venue will be ready by Dec 20 in time for an inauguration on Jan 15.

In addition to hosting England's game with Italy, Manaus will be the site of Cameroon's pool match with Croatia on June 18, Germany vs the United States on June 22 and Honduras vs Switzerland on June 25.